The invention relates to a method of recording signals on a record carrier of a type that can be overwritten. Information patterns of optically detectable marks are recorded on the record carrier in substantially parallel tracks. The tracks are scanned by a radiation beam, and the marks are obtained by the radiation beam locally heating a suitable recording layer of the record carrier. The energy contents of the radiation beam are set in response to detection of undesired signals from a test information pattern recorded with the radiation beam.
The invention further relates to a recording device for recording signals in substantially parallel tracks on a record carrier of a type that can be overwritten. The recording device comprises a scanning unit for scanning the tracks with a radiation beam for the purpose of introducing in the tracks information patterns of optically detectable marks which correspond to the signal patterns; and a setting unit for setting the recording intensity of the radiation beam with the aid of a setting signal to be applied to the setting unit, the setting signal being dependent on the detection of undesired signals from a test information pattern recorded with the radiation beam.
A similar method and device for recording signals on a record carrier is known from European Patent Application No. ("EP-A") 0 400 726. The method and recording device described in that application give a procedure for media calibration by which a recording intensity is determined for a radiation beam by which information patterns are introduced in the recording layer of a record carrier. The media calibration described in EP-A 0 400 726, comprises the following steps:
a. a first information pattern having a first frequency is recorded in a track with a maximum recording intensity of the radiation beam; PA0 b. then, in the same track, a second information pattern having a second frequency is recorded with a low, minimum recording intensity of the radiation beam; PA0 c. then, the information recorded in the track is read out and, the read signal is applied to a detection mechanism tuned to the frequency of the first information pattern; PA0 d. if signal rests of the first information pattern (having the first frequency) are still detected, steps b to d are repeated, the recording intensity for each repetition being increased by a specific desired randomly selectable step.
Once rests of the first information pattern (having the first frequency) are no longer detected in step d, an intensity setting of the radiation beam is found at which there is a guaranteed minimum error rate of the information pattern to be recorded and subsequently read out.
What has just been described is illustrated with reference to FIGS. 7 and 8 of EP-A 0 400 726, with FIG. 8 representing an error rate characteristic as a function of the intensity of the radiation beam used for recording. The method and device described in EP-A 0 400 726 provide a setting of the radiation intensity which is situated substantially in the middle of a flat domain of the error rate characteristic in which the error rate is low. Although this provides a highly reliable recording of information patterns, with a very low error rate, there are nevertheless several inherent disadvantages, for example: specially designed hardware is necessary for generating the information patterns having a first and a second frequency, and for detecting the rests of the first information pattern (having the first frequency). A further disadvantage is that the first information pattern (having the first frequency) is recorded with full power of a laser diode which generates the radiation beam. Having the laser diode operated at full power is disadvantageous in that this shortens its useful life.